This invention relates to an improved preparation of Wittig salts of alpha,beta-unsaturated alcohols. The Wittig salts are useful intermediates for synthesizing polyene compounds, such as vitamin A.
Wittig salts of alpha,beta-unsaturated alcohols have heretofore been prepared by treating the alcohol with a phosphine salt of a strong mineral acid, such as hydrochloric acid. See, for example, German Patent No. 1,059,900. Such preparations of Wittig salts have not however been entirely satisfactory. The use of strong acid salts under acidic conditions and in the presence of an unsaturated aldehyde has been found to cause alpha,beta-unsaturated alcohols to dehydrate and/or rearrange. As a consequence, the yields of Wittig salts from such processes have been relatively low due to the formation of dehydration and/or rearrangement by-products.
The formation of by-products has been a particularly severe problem in preparing Wittig salts of tertiary alcohols, wherein the hydroxy group is quite labile and the alcohol is hence quite prone to undergo rearrangement and/or dehydration. In this regard, it has been found that by utilizing, the process disclosed in German Patent No. 1,059,900, the yield of the Wittig salt of vinyl-beta-ionol has been quite low. This means that the overall process furnishes an improved polyene end-product with regard to purity and yield.
There has been an unfilled need therefore for an improved method of producing Wittig salts of alpha,beta-unsaturated alcohols.